The present invention relates to a method for measuring the fuel pressure prevailing in an electromagnetic injector of this fuel in one of the cylinders of a direct-injection internal combustion engine, the injectors associated with the said cylinders being supplied with fuel via a common supply manifold and their open times being calculated and controlled by a computer.
In FIG. 1 of the attached drawing there is illustrated a known type of fuel-supply device of a direct-injection internal combustion engine comprising a fuel tank 1, a pump 2 supplied by tank 1 and associated with a pressure regulator 3 for delivery of the fuel to a second pump 5 via a filter 4, the fuel delivered by pump 2 being brought to a first pressure level that is higher than atmospheric pressure but is relatively low, so that pump 2 is referred to as the xe2x80x9clow-pressure pumpxe2x80x9d. Second pump 5 raises the fuel pressure once again to a second level higher than the first, suitable for supplying fuel injectors 61, 62, 63, 64 mounted on a fuel-supply manifold 7 of the cylinders of a direct-injection internal combustion engine (not illustrated).
The pressure of the fuel delivered by pump 5, referred to as the xe2x80x9chigh pressure pumpxe2x80x9d, is fixed by an electromagnetic regulator 8, such as an electric valve controlled by a computer 9. In this latter case, a sensor 10 delivers to computer 9 a signal representative of the pressure of the fuel contained in manifold 7, to permit the computer to ensure regulation of the fuel pressure in this manifold at the required predetermined level. Computer 9 is commonly composed of the operational management computer of the engine, which among other tasks controls injectors 6i (i=1 to 4 in the illustrated example), and especially the open time thereof.
The fuel not delivered by injectors 6i is returned to the tank via a conduit 11, 12 maintained at atmospheric pressure.
The quantity of fuel that must be injected by a particular injector into the associated cylinder of the engine is calculated by computer 9 as a function of a certain number of well known parameters. The computer also determines which open time of the injector is appropriate for ensuring that a predetermined quantity of fuel will enter the cylinder. This open time is a function not only of this quantity but also of the fuel pressure that prevails in manifold 7 and that fluctuates in time despite the presence of regulator 8.
As seen hereinabove, this can be composed of an electric valve controlled by computer 9, to establish a discontinuous escape of fuel appropriate to ensure regulation of the fuel pressure at a predetermined level.
Whenever one of injectors 6i opens to introduce fuel into the associated cylinder, this opening action creates in manifold 7 a second escape of fuel, the consequences of which are illustrated in FIG. 2. In this figure, 6i represents the timing diagram for opening of injector 6i under consideration for a time Ti, and P represents the graph of the pressure P of fuel in the manifold as observed during and around the opening of this injector. As illustrated, after the moment t0 of opening of the injector, the pressure P in the manifold drops because of the resulting escape of fuel, and this possibly continues until the moment tf=t0+Ti at which the injector is closed, the pressure being restored to its previous stable level only after an additional time interval.
To allow for this pressure drop, it is proposed in French Patent No. 2715440 of the Applicant that the pressure prevailing in a fuel injector during the open time thereof be measured continuously in such a way that the computer can deduce therefrom, by integration, the quantity of fuel actually injected into the cylinders during this open time of the injector, and that the injector be signaled to close when the quantity of fuel to be introduced has been reached.
This method requires, however, that the fuel pressure in the manifold be measured continuously or at least that this measurement be performed with very high sampling frequency, compatible with the very short open time of the injectors (several ms).
In addition, the opening of an electromagnetic injector requires an electric current of high intensity, which generates strong electromagnetic perturbations that can falsify the measured signal transmitted by pressure sensor 10 during this opening action.
The objective of the present invention is to provide a method capable of measuring with good precision the fuel pressure prevailing in an injector of this fuel in a direct-injection internal combustion engine, this method not suffering from the disadvantages of the prior art technique indicated hereinabove.
In particular, the objective of the present invention is to provide such a method that permits pressure measurement at common sampling frequency while being insensitive to the electromagnetic perturbations prevailing in the surroundings of the pressure sensor used.
This objective as well as other objectives of the invention that will become evident upon reading the description hereinafter is achieved with a method for measuring the fuel pressure prevailing in an electromagnetic injector of this fuel in one of the cylinders of a direct-injection internal combustion engine, the injectors associated with the said cylinders being supplied with fuel via a common supply manifold and their open times being calculated and controlled by a computer, this method being noteworthy in that a) any overlap of the open times of at least two of the said injectors is detected, b) in the absence of such overlap, the fuel pressure in the manifold outside the open time of the injector under consideration is recorded, c) in the presence of such overlap the fuel pressure upon opening of the injector under consideration is recorded, and d) the recorded measurement is corrected as a function of a predetermined variation of fuel pressure induced by the opening of the injector or injectors.
As will be seen in detail hereinafter, this method makes it possible, on the basis of a pressure measurement that is reliable, since it is not perturbed, to know precisely the mean pressure prevailing in a fuel injector while this is delivering fuel. It is then possible precisely to adjust the open time of the injector to a value appropriate for it to deliver a quantity of fuel determined by the computer.
According to another characteristic of the method according to the invention, there is applied to the recorded measurement, in stage d) hereinabove, a decrement that is a function of the measured pressure and/or of an estimate of the open time of the injector.
According to another characteristic of this method, when it is used for calculation of the open time of the injectors of the engine, there is applied to the open time calculated on the basis of the recorded pressure an increment that is a function of the calculated open time and of the recorded fuel pressure.